Stirling Engine

I'm probably not interested in joining your team (I live in the US, and that's not my area of expertise, in general), but I might be interested in buying an engine, depending on its specs and final cost.

I'm interested in finding small stirling engines like that that could be used to drive a small generator using the heat output from solar collectors of various sorts (i.e., either concentrating or non-concentrating, then using the waste heat to help heat my home or hot water. I'd probably need concentrating collectors to get a reasonable amount of electrical energy.

I might also use it somehow on or near a coal fired boiler or stove to try to make some use of waste heat.

I am confident of selling one to you which will meet your needs by the end of this year along with a solar cocentrator of 1 mtr dia. can you mail me your email id so that we can keep you posted of our progress tech and cost wise?

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Sorry but Bangalore is a little bit far for me to join your troop. How much mechanical design skill do you need? Why don't you simply either buy a built engine, buy a kit to make an engine or if you just wish to test your machining and assembly capabilities buy an existing design?

How about being a tech/nontech team member online?

chandu

How about you answer my questions first? If your really want my help you'll start by answering some simple questions.

We have abundant machining capabilities here at Bangalore. We are however accurately short of designing people. This is because Stirling engine is very low amongst the engineering community. Will be happy to answer more questions

By Googling "Stirling Engines" you can find a wealth of individuals who have made small engines like this. Some of their techniques may be helpful.

I do regular search. Apart from the toy models there is not much on half hp and above engines. Thank you for your response.

Re: I do regular search. Apart from the toy models there is not much on half hp and above engines.

I should have probably mentioned some of this earlier. I don't want to discourage you, but developing a 1.25 hp Stirling engine is probably going to be neither easy nor inexpensive. I hope I'm wrong!

I've done some "research" on this. (Ok, it amounts to an "Internet literature search" ;-)

I put some notes on a previous CR4 thread--see Re: Looking For Practical Sterling Engine Design Resource--you should look at that, but I've found some other stuff since then that might give you a better idea what you're facing.

Oh, by the way, with respect to the 2nd bullet on that post, I've since become certain that his efficiency calculations are wrong. He did the calculation using degrees Celsius--the calculation has to be done with an absolute temperature scale, like Kelvin or Rankine. (At the time I wrote that post, I thought what he did was wrong, but I wasn't certain, now I'm certain.)

One of the things that I think will be useful to you is to watch this Youtube video: PHILIPS STIRLING CYCLE GENERATOR. What you should notice includes this:

• this is a compact (more below) commercially built Stirling engine and built in generator (so people have made commercial products--my suspicion (and maybe they even said this, I didn't rewatch the entire video) is that it was built, perhaps during WWII, to power radios (behind enemy lines?) because batteries were just not suitable (if the batteries were rechargeable, they'd need a means to recharge them, so having a powered generator just eliminated one thing from the equation)
• 
  
• anyway, by looking at it, I would have guessed that it was about the same size and weight as a 2 kw gas powered portable generator that we might buy here in the states for emergency use--instead, it seems to be rated at about 200 watts. (I base that on the generator that the engine drives, the narrator said the generator develops about 200 watts at 220 volts.)
• 
  
• so, a Stirling engine might be very energy efficient, but it is not particularly space or materials efficient. Not being materials efficient means probably increased cost of materials over some design that is more materials efficient, although you might get by with less expensive materials depending on the operating temperature that you choose--if it is less than that of an IC engine, you might be able to use some less expensive materials.
• 
  
• Otoh, some people talk about building (or, really converting) IC engines to Stirling, starting with lawnmower or automobile engines. Because those are well up on the production curve, they are fairly inexpensive. I haven't seen a statement in writing, but just based on what I mentioned about the generator in the Youtube video, I might guess that if you convert something like that to a Stirling engine, you might get 1/10 the power output that the engine was rated for (assuming you use a high enough operating temperature, and operating gas pressure. (IIRC, the guy working on converting two 6 cylinder automobile engines to a Stirling engine is talking about operating pressures between 10 and 80 bar. The commercial engine in the Youtube video seems to use pressures between 11 and 14 bar.

Some other links:

• Stirling Engine: this is the project to convert two 6 cylinder automobile engines to a Stirling engine--joining the two into one common crankshaft with one displace 90 degrees from the other--one bank of cylinders is the hot bank, the other bank is the cold bank--IIUC, much piping must be added between each pair of cylinders (one hot, one cold)
• Great Stirling engine Links (from the American Stirling Company)--I guess this appears to be primarily a model site, but they do have links to some stuff that might be useful, a book about a 5 Hp engine (I assume that is about instructions to build one), an FAQ which has some useful information (read it), a link to a New Zealand Company that sells a CHP (Combined Heat and Power) unit that includes a Stirling engine--I didn't look today, but my vague recollection is that it sells for something like $20,000 (don't know whose dollars those might be)
  

There is another company that sells a commercial product something like the Whispergen CHP, but I can't find a link to that atm.

Finally, take note of this paragraph, from UNDERSTANDING STIRLING ENGINES:

It is important to recognize that the Stirling engine is a high-temperature machine. It cannot run well on the low temperatures available from simple flat plate solar collectors. It must use a concentrating, sun-tracking solar collector. This device adds considerably to the cost and maintenance requirements of the system. Also, such a device does not make use of the diffuse component of solar energy, only the direct component. So hazy sun is not good enough. Bright, clear skies are needed before the concentrating collector will develop the high temperature necessary to operate the Stirling engine. For all these reasons, Stirling systems using concentrating, sun-tracking solar collectors will be much more expensive and will require more care in their operation than those using fuel as their heat source.

Here's a quote from Wikipedia: Stirling engine--I guess Disenco is the name of the other company I was looking for:

Disenco, a UK based company are going through the final stages of development of their HomePowerPlant. Unlike other m-CHP appliances coming to market the HPP generates 3 kW of electrical and 15 kW of thermal energy, making this appliance suitable for both the domestic and SME markets.

WhisperGen, a New Zealand firm with offices in Christchurch, has developed an "AC Micro Combined Heat and Power" Stirling cycle engine. These microCHP units are gas-fired central heating boilers which sell unused power back into the electricity grid. WhisperGen announced in 2004 that they were producing 80,000 units for the residential market in the United Kingdom. A 20 unit trial in Germany started in 2006.

Hmm, by now, I've copied most of the stuff from that earlier post to here. Skipped at least one link about a Stirling engine from a lawnmower engine. I'll leave it there. ;-)

I hope this helps. If I've mentioned something that you can't find a link for, let me know and I'll see if I can find it.

Thank you very much for the valuable information and we appreciate the time you have given.

Philip's had designed and developed some sterling engines before the second world war. One was specially made for automobile and could develop 200 hp. They suddenly dropped the project but they have a number of patent connected with high hp engines

There has been some remarkable break through in metallurgy in India for need of space and aeronautical sector requirement which are extremely cost effective and has the thermal properties suitable for Stirling engine. Our trials with this material has been good.

Since car engines are internal combustion engines they cannot be economically be converted into a stirling which happens to be an external combustion engine.

I will follow up on the links provided and get back to you with my observation and also tell you about the stirling engine our team will have in about six months time

When you get to youtube, check out several of the videos about Stirling engines. There are some that might give you some ideas. I saw one where they built a Stirling engine starting with a two cylinder pump--it looks like it would be a fairly easy thing to do, and give you some insights into how to adjust a design like that to get close to 1.25 Hp.

Something else I noticed--I guess it is what you're planning, but many of the ones that used the sun, ran directly off sunlight (concentrated by a parabolic reflector). I was thinking in terms of heating water, then using the hot water to drive the engine. I might still think in those terms as the "waste" hot water can be heat for my home and hot water.

We are working on the same route - solar and bio mass(gas as well as direct) a hybrid heating system . We have this ready till 500 - 600ºC heat range. We have two fractional hp stirling based on Fernando design which we are upscaling to 1 to 1.5 hp by incorporating a regenerator. We need to come out with a prototype design of the regenerator as the ones we have experimented with are not satisfactory mainly because of materials have not been the right one. Any suggestion on how we can solve this technical shortcoming?

Could you please do the favor of turning off the boldface and italics, except for words or brief phrases that need emphasis?

Sorry about the types. Will chang starting with response.

Re: We need to come out with a prototype design of the regenerator as the ones we have experimented with are not satisfactory mainly because of materials have not been the right one.

As I understand it (AIUI), what the regenerator needs to do is, as air is moved back and forth through it by the movement of the pistons, absorb heat from hot air in one part of the cycle, and release that heat to colder air in the other part of the cycle.

I don't know what you've tried so far. In the descriptions of Stirling engines that I've noticed so far, the regenerator has usually consisted of some kind of metallic wool (e.g., steel wool) packed into a tube open to the two pistons. I don't know how densely the wool is typically packed--presumably you want good turbulent flow so the air comes in contact with the metal fibers, but not packed so tightly as to create too much resistance.

I'd expect that all of these factors could be considered and might lead to a better regenerator:

• conductivity of the metal--I would think the more conductive the better
• not too low a melting point of the metal--you wouldn't want it to melt and clog the pores. But wait--one design (was it the 12 cylinder being built from two auto engines) used had what they called a metal foam in (iirc) both the hot and cold pistons--I don't know for sure if it was serving as the regenerator or not, but you might dig into that. I think the metal foam was based on lead, which has a low melting point.
• the size of the metal fibers--there's probably a balance between being small for fast conduction but not so small that individual fibers might melt (and clog the pores)
• the heat capacity of the fibers--you want enough metal to absorb all the heat from the hot gas if possible
• I would think there is no real restriction on the size of the regenerator--I've seen some small ones, but I think some of them could be bigger--I don't know whether it would be best to have the volume of the regenerator sized to hold about the exhaust volume from the hot cylinder, or something greater than that--I don't think you want it smaller (but it's hard to explain why I think that, or whether I'm right)

The whole thing is a heat transfer problem.

I would expect that you'd want to insulate around the outside of the regenerator--the one thing that doesn't do any good (I think) is leaking heat out of the engine system (except, obviously, at the cooler).

I could be all wrong, I just thought it might be helpful to think out loud about the requirements for the regenerator.

We tried a number wool form. This was steel,copper,aluminium and other alloys and it works reasonably well till the engine reaches an rpm of 300 - 350. Higher rpm cycle the wool in the regenerator is not able to synchronise in transferring the heat. It appears we have to come out with a combination of heat exchangers incorporated into a single unit. Like wool and metallic tubes in combination. Our test trials of such a hybrid regenerator appears like a solution. There are some composit materials in the world market used for other thermal application and this could be suitable to try out for our upscaling.

Re: This was steel,copper,aluminium and other alloys and it works reasonably well till the engine reaches an rpm of 300 - 350. Higher rpm cycle the wool in the regenerator is not able to synchronise in transferring the heat.

Yeah, that makes sense (that at some speed point, the bottleneck would be the time to absorb and release heat in the regenerator).

So, I guess the obvious ideas are things to speed up that heat transfer--smaller fibers, better (faster?) conductivity, ...

What speed do you want to achieve? Hmm, I guess for a generator, you may want something like 1800 (1500?) or 3600 (3000) rpm?

Or:

• you could look for generators with lots of poles (or build your own--"hobbyists" do that for wind generation--I could point you to some sources or search the web)
• a gear "reducer" (well, increaser)

About 600 rpm should be good with a good torque charecteristics so that the engine has power as driver unit for 3 - 6 kw generator.

I thought this was a 1.25 hp engine; if so, 3-6 kw will be impossible.

So often people get trapped by exactly that kind of a detail. 1.25 hp is only 932 watts of power. To get into the range that he wants, he'll have to have an engine capable of at least 8.75 hp when you consider the likely generator efficiency.

As far as the frequency output of this engine, I think worrying about that is a red herring problem that will just complicate the problem of running the engine at an optimal speed. A Stirling engine does not throttle well because of the nature of the slow rate of heat transfer of various parts. Because of this, trying to change the engine speed to match the grid frequency seems impractical if not impossible to me.

The engine will be the driver of the 3kw generator. stirling will not be the generator.

You're getting slow Red - 30 posts to arrive at that conclusion.

I try to give people the benefit of the doubt. But you're right that I should have known better when my earlier questions remained unanswered. Sigh.

How do you plan to get a 1.25 hp engine (no matter what type) to drive a 3+ kw generator? No amount of passion will get you past this over-unity obstacle, even if you were to get say MS Divekar on your team.

What passion can do is to focus emotional energy so as to blind the passionate person to uncomfortable truths. By the way, a 1.25 hp engine can drive a 3+ kw generator if the definitions of the two different devices are not compatible. For example, if the engine power is selected as (say) the power output at highest efficiency, and the generator rating is selected as the maximum available power output. The engine can put out more than 1.25 hp at it's maximum, and the generator can put out less than 3+ kw (if field strength is variable). maybe this passion is blind. I would suggest that we not hold our breaths while this development occurs.

Of course a 1.25 hp engine could conceivably drive a 3+ kw generator if the generator happens to be loaded only to about 0.9 kw. But that would be meaningless and silly. Perhaps that can be overcome by spirituality and meditation, to say nothing of levitation?

We are coupling number of engines to drive 3 to 5 kw generators.

Bit harsh - at least it recognizes Stirling has scale and speed limitations deeply embedded in thermodynamics - so it's sort of something - or more than most Stirling aficionados* seem to grasp.

He could hook up a few dozen of these - assuming he adds more to overcome the losses in power transmission.

_{*read; brainless-over-unity-hobbits}

We plan to use the 1.25hp engines in tandem mode to drive the 3hp generator.

My understanding is this:

chandu (and associates) want to get into the field of solar thermal electric power.

I've seen other posts or Internet references to them having done some things related to solar heating (or cooking), iirc.--This is sort of an expansion of that.

As such, at this point they don't know how big a Stirling engine (and then a generator) they can drive from a given size reflector.

I would guess the the size of the Stirling engine and generator will be determined by the practical size(s) of the reflector they wish to build.

So, I'd like to cut them some slack.

For illustration, assume insolation is 1 kw/m². The projected area of a Φ1m reflector ≈ 0.7854 m²; this would be ~1.05 hp, but only if efficiency is 1.00.

That, I'm sure, should be helpful.

Then using efficiency = 1 - Tmin/Tmax (in degrees Kelvin or Rankine), and maybe a hot side temperature of 300 degrees C (573 K) and a cool side temperature of 90 degrees C (363 K), the theoretical efficiency is around 37%. I'm sure they won't achieve that--maybe 20%, so maybe they could hope to get 0.2 hp out of a 1 meter reflector.

Assuming 100% area, focus and absorption (at midday, cloudless)

Intresting. Conclusion drawn on assumed input. Here is our actual data in our part of the world, South India situated between equator and 21°N and a platuea of average 2000ft above msl. Solar energy flux per sq.m is on an average ranges from 1500 - 2000 watts depending on the location. The stirling engine on our table operates with cold part at 40°C and the hot part at 300 with the heat supplied by hybrid system of solar and bio -gas. You guys have to get out of US centered tech data input especially for working with heat engines. You have the right ideas but are in the wrong place of the globe. So what is the next step apart from scoring brownie points? My suggestion join hands and move forward to create a win-win situation for ordinary people of the world.

Is that a 24-hour average that includes night time? Or a yearly average that includes winter?

This project looked interesting at the beginning, but the more you say, it appears the less you know.

We have 11 to 12 hrs of daylight all the year round unlike in the northern latitude which varies very widely between summer and winter thus Europe and USA has daylight saving time system. That is not the case in places near the equator. We dont have winter but very warm,hot and hottest range(25 - 45°C) of temperature.

The daylight saving time system is a "red herring" that has nothing whatsoever to do with this. More to the point, how cloudy is the monsoon season, and how much does it reduce the useful insolation?

monsoon lasts for 10 -12 weeks. It is not uniform and about 10 days in a month does the parabola as a solar heater becomes redundant. Back up sources during such period is bio gas generators. Why is daylight saving a red herrring?

Re: Why is daylight saving a red herrring?

Humans setting up an arbitrary time scale, or changing it, does not effect how much the brightly the sun shines or how many hours it shines during the day, it only affects what time, on the human scales, the sunshine occurs.

I agree with you. But northern latitudes gets less sunlight per year compared to the amount of sunlight near the equator.

True. (But again, Daylight Savings Time doesn't change the amount of sun per day at either the equator or at latitudes other than the equator.)

Since the suns rays reach northern latitude at an acute angle its energy is absorbed by the atmosphere compared to countries 21°N or S. Energy density loss gets coupled with dull sunlight. I have seen this in Wn and ND and also in England while collecting data at different northern latitudes.

True. (Still, nothing to do with DST.)

Also, that (what you describe) is why there are tables that give solar insolation values for various locations. (I.e., why you get close to 2000 watt / m^2 and I only get about 1000 watt / m^2.)

Re: Intresting. Conclusion drawn on assumed input. Here is our actual data in our part of the world, South India situated between equator and 21°N and a platuea of average 2000ft above msl. Solar energy flux per sq.m is on an average ranges from 1500 - 2000 watts depending on the location. The stirling engine on our table operates with cold part at 40°C and the hot part at 300 with the heat supplied by hybrid system of solar and bio -gas.

Thanks for the additional data. I didn't have the data before now, so I took a guess.

Re: You guys have to get out of US centered tech data input especially for working with heat engines.

Withholding comment.

Here are a few, including two in your size range. So it certainly can be done. It will be interesting to see the various designs that may emerge fairly soon. The model railroading field may have some steam designs that could be adapted, along with many blogs about machining techniques, etc. Best of luck with this!

Hello Tornedo. Thanks for the response but the links were missing.

chandu

It helped a lot with some valuable info especially the cost per kw. We will have an unbeatable combination of engine quality,output and cost. Thanks.

Power in peoples hand!!

The concept of the development of an engine which can use available heat at a significant level of efficiency is a desirable goal. When the history of engine development is considered, internal combustion (obviously) has been a major focus. Have you looked at this history? The OP is looking for design skill but made a major error in choosing to use a Stirling engine without understanding the limiting effects of that choice. Start over.

Look at what skills and technological resources you have on hand and what your goals are. Are you aiming at a marketable product? External funding? Fun? The design resources available to you gratis on the net is huge, but if what you need is a project leader, competent people will need a reason. What is it?

Passion for the project technically and a will to succeed,

I designed a solar concentrator with dual axis tracking for a sterling engine. We started with designing a stirling engine and ended up borrowing one. The link which I provided has lot of details and Schmidt theory. I have the detailed calculation in " mathcad" file. If needed I can send you that. Take a look at this link. very helpful.
www.bekkoame.ne.jp/~khirata

Also check this
http://www.btinternet.com/~sylvestris/fizgign/fizindex.htm
If you just want to build one use the above. Keep me in the link. Good luck.

Thanks Raam. Will keep you posted Can you give us the performance sheet of trial of your borrowed stering and parabola. We are particularly interested in power output of the engine.

SOUNDS INTERESTING CAN THE ENGINE BE RUN ON GREEN FUEL?I HAVE THE METHOLD FOR FUEL INDUCTION MAYBE WE CAN TEAM UP AND DEVELOPE TOGETHER CAN YOU EXPLAIN MORE ABOUT YOUR ENGINE? ED MARTINEZ M.L.D {MOLECULAR LINEAR DYNAMISIST}

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thank you..

Yes it can run on green fuel. While most of the engine in use is internal combustion engines, stirling is an external combustion engine. That is fuel is not injected into the engine but is converted to heat externally and this heat drives the engine. So any temperature difference becomes the fuel. Greater the temp. difference more efficient and gives higher hp. I can send more detailed info in video of the engines we have on the table. We will be happy to team up with you. How do we go about it?

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Could you please do the favor of turning off the boldface and italics, except for words or brief phrases that need emphasis?

(Déjà vu.)

Posting email addresses is inadvisable, unless you like spam.

We went to develop Sterling Engine and ended up developing a Nano & Micro Steam Turbine Generators. To the best our knowledge, we are one of the very few in the world who supply steam turbine generators from 1 KWH to 100 KWH. You have to supply 10 bar saturated steam to drive the turbine.

The unit comes as a CHP Unit with a discharge steam of 120C at 1 bar and the steam cosumption is 25 Kg per KWH.

Interested? Do contact me at to discuss more.

Best wishes,

Mizun

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We are interested. Let us start our discussion on cr4 internal messaging system. Looking forward to your response

Please use correct units: kW rather than kWh for power output. Also "Stirling" rather than "Sterling."